1. Field of the Invention
The present invention pertains to a technology for a pixel circuit for a current-driven light emitting element.
2. Description of the Related Art
Electrooptical devices that use organic EL (electroluminescent) elements have been developed in recent years. Because an organic EL element is a self-emitting element and does not require a back light, it is expected to enable the production of display devices having low power consumption, a wide field angle and a high contrast ratio. In this specification, an “electrooptical device” means a device that converts electrical signals into light. The most common implementation of an electrooptical device is a device that converts electrical signals that represent an image into light that represents an image, and this type of device is preferred for display devices in particular.
Existing types of organic EL element pixel circuits include pixel circuits that use the voltage programming method that sets the light emission tone based on the voltage value and pixel circuits that use the current programming method that sets the light emission tone based on the current value. “Programming” refers to the process to set the light emission tone in the pixel circuit. The voltage programming method is relatively fast, but it can result in somewhat inaccurate light emission tone setting. On the other hand, the current programming method sets the light emission tone accurately, but can require a relatively long time to execute.
Accordingly, a pixel circuit that uses a method different from either of the conventional methods has been desired. This demand exists not only for display devices that use organic EL elements, but also for display devices or electrooptical devices that use current-driven light emitting elements other than organic EL elements.